Try the following stes to troubleshoot ADSL issues:
1)The ADSL line is connected and is using pins 3 and 4. For more information on the ADSL connection, see the hardware guide for your router.
2)The ADSL CD LED is on. If it is not on, the router may not be connected to the DSL access multiplexer (DSLAM). For more information on the ADSL LEDs, see the hardware installation guide specific for your router.
3)The correct Asynchronous Transfer Mode (ATM) virtual path identifier/virtual circuit identifier (VPI/VCI) is being used.
4)The DSLAM supports discrete multi-tone (DMT) Issue 2.
5)The ADSL cable that you connect to the Cisco router must be 10BASE-T Category 5, unshielded twisted-pair (UTP) cable. Using regular telephone cable can introduce line errors.
Refer the "configuring ADSL" section in the link given below for more information on ADSL config on cisco 876 router:
http://www.cisco.com/en/US/docs/routers/access/800/850/software/configuration/guide/857sg_bk.pdf